This invention relates generally to heat-exchanger systems for fireplaces, and more particularly to circulation systems of the type employing one or more boiler devices, adapted to be located within the firebox.
In the past a number of heat-extraction systems have been proposed for use with fireplaces, having met with varying degrees of success. Several popular prior devices comprise those incorporating hollow gratings through which air or water is circulated. The air or water is heated by the proximity of the grate to the coals of the fire. Blowers and the like are also used with some prior units, while others employed natural convection.
One of the problems associated with most prior installations was that the efficiency of the heat-extracting process was extremely low. With forced air gratings, the fireplace has to be used without a screen or enclosure. This meant that a large quantity of air from the room was being drawn up the chimney, only to be replaced by colder air which seeped into the room from the outside, through minute cracks around doors and windows. The small amount of heat obtained from such gratings did not nearly compensate for the loss up the chimney. As a result, the overall heating efficiency of these arrangements was poor. Moreover, in systems where heat was extracted from the coals as in the case of a circulating-air type grate, the combustion temperature of the fire was significantly reduced. Accordingly, the use of such grates has been found to detract from the overall efficiency of the system, since it has been determined experimentally that less heat per pound of fuel is being produced, where such systems are employed.
Efforts to limit the flow of air from the room by the use of glass enclosures greatly increased the combustion efficiency of the fire. However, in the majority of installations heretofore known, the overall heating efficiency was still inadequate; most of the heat contained in hot gases from the fire was merely being drawn up the chimney.
Other installations involved integral heating systems comprising networks of pipes contained in the walls of the firebox, through which water was circulated to provide the necessary transfer of heat. The external plumbing often associated with such networks was aesthetically unattractive, as well as representing substantial costs involved with installation and maintenance.